The present invention relates to a method for detecting a low molecular weight compound by utilizing a quartz resonator, more particularly a method for detecting a low molecular weight compound in a solution with high sensitivity by utilizing a quartz resonator.
Generally, a quartz resonator analyzing apparatus comprising a quartz resonator, oscillating circuit and frequency measuring device is applied for the analyses of various substances in solutions, because the change in mass of a substance to be detected which is adsorbed on the surface of the quartz resonator is precisely grasped as the shift in the oscillating frequency. In recent years, there have appeared many proposals for more speedily detecting the change in mass and concentration of a substance to be detected by fixating, on the surface of a quartz resonator, various adsorptive films having adsorptivity for a substance to be detected.
These methods, however, are mostly ones for high molecular weight proteins that utilize antigen-antibody reaction or ones that make use of latex coagulation reaction, and at present there has been proposed no detection method effective for a low molecular weight compound in a solution, for example, porphyrin.
The present invention, which has been accomplished under the above circumstances, is aimed at providing a method for detecting a low molecular weight compound in a solution with high sensitivity.
The inventors found that, when an adsorptive film (A) for a low molecular weight compound is formed on the surface of a quartz resonator and such a film (A) is also formed on the surface of a signal enhancing material and when a solution of a low molecular weight compound is introduced in this measuring system, the low molecular weight compound is captured sandwich-wise efficiently between these films (A), and thus the inventors accomplished the present invention.
Namely, according to the present invention, the following inventions are provided.
(1) A method for detecting a low molecular weight compound in a solution which utilizes a quartz resonator and which comprises capturing a low molecular weight compound between an adsorptive film (A) for a low molecular weight compound provided on the surface of a quartz resonator and an adsorptive film (A) for a low molecular weight compound provided on the surface of a signal enhancing material and comprises detecting the shift in frequency of the quartz resonator before and after the capture.
(2) A detection method according to the above (1), wherein one molecule of a low molecular weight compound to be detected is combined to plural molecules of a material for forming the adsorptive film.
(3) A detection method according to the above (1) or (2), wherein the material for forming the adsorptive film (A) for a low molecular weight compound is a peptide.
(4) A detection method according to the above (3), wherein the peptide is an oligopeptide.
(5) A detection method according to the above (4), wherein the oligopeptide is one obtained by a combinatorial chemical technique.
(6) A detection method according to any one of the above (1) to (5), wherein the signal enhancing material is synthetic resin beads.
(7) A detection method according to the above (6), wherein the synthetic resin beads are polystyrene type beads.
The detection method of the present invention is explained concretely hereinafter.
[Quartz Resonator]
The quartz resonator used in the present invention is preferably one comparatively inexpensive with a frequency of about 5 to 10 MHz, since, although the higher its basic frequency the greater the response for oscillating frequency, such a high frequency type causes noises to increase, frequency stability to become lower and the unit price of the resonator to rise.
For a quartz resonator to be oscillated stably in a solution of a signal enhancing material, if only one side of the quartz resonator is made to touch to the solution, this suffices for it. And, for example, a technique is adopted wherein one side of the quartz resonator is affixed with a quartz piece using a silicone adhesive or covered with a silicone material.
As electrode materials for the quartz resonator, silver or gold is preferable. From the viewpoint of the magnitude of frequency response and the cheapness of price, silver is favorable. But from the viewpoint of the high level of frequency stability in solution and the resistance against oxidation of the electrode surface during preservation in the air before use, gold is more favorable.
[Low Molecular Weight Compound to be Detected]
As the low molecular weight compounds to be detected according to the present invention there are enumerated those that can combine with plural film forming materials in a monomolecular state, namely, low molecular weight organic compounds having symmetric structures, such as porphyrin, dioxin, PCB and the like.
These low molecular weight compounds are usually used in the form of being dissolved or dispersed in solvents, but preferably used in the form of solutions.
As the solvents, any can be employed as long as it dissolves or disperses the low molecular weight compounds. Such solvents include water and organic solvents such as alcohols and DMSO. A solvent having low polarity is usable, and, in that case, covering one side of the electrode, which has been mentioned above, is unnecessary.
[Formation of Adsorptive Film (A) for Low Molecular Weight Compound on Surface of Quartz Resonator]
In the present invention, there is provided, on the electrode surface of a quartz resonator, a film (A) having adsorptivity for a low molecular weight compound to be detected.
The film (A) may be any material as long as it has adsorptivity for the low molecular weight compound.
Materials for forming such a film include those which does not differ significantly in terms of molecular weight from low molecular weight compounds such as peptide, DNA and the like. The film forming material preferably used in the present invention is peptides.
As the method of forming the film, all the hither to known methods can be used such as dip coat method, spin coat method, casting method, LB method, self-assembled monolayer film forming method and the like.
The above-mentioned film (A) is preferably formed so that it may be oriented uniformly on the whole surface of the quartz resonator. However, the film is not necessarily formed uniformly on the surface if it can adsorb the low molecular weight compound of detection target and can pinch/capture the low molecular weight compound in cooperation with the film (A) provided on the latex beads (signal enhancing material) mentioned hereinafter.
The surface of the electrode of the quartz resonator sometimes has contaminants stuck thereon, and upon forming the film it is desirable to clean beforehand the surface of the quartz resonator with a suitable means, for example, with a peroxide solution.
[Formation of Adsorptive Film (A) for Low Molecular Weight Compound on Surface of Signal Enhancing Material]
In the present invention, on the surface of a signal enhancing material the adsorptive film (A) for low molecular weight compound is provided.
As the signal enhancing material, any of the heretofore known carriers can be used, such as synthetic resin beads, proteins, liposomes and gold colloids, as long as it has a large mass and allows the film (A) to be formed on its surface.
Among these, the synthetic resin beads can be put to reuse by a simple washing operation and are preferably used in the present invention.
As the synthetic resin beads there are enumerated beads formed from various resins and copolymer resins such as polystyrene type resin, polybutadiene type resin, polyethylene type resin, polypropylene type resin, polyisobutylene type resin, poly (acrylic acid) type resin, poly (methacrylic acid) type resin, poly (methyl methacrylate) type resin, poly(ethyl methacrylate) type resin, poly(propyl methacrylate) type resin, polyacrylamide type resin, poly(vinyl alcohol) type resin, poly (vinyl chloride) type resin, poly(vinylidene chloride) type resin, poly(maleic anhydride) type resin, poly(vinylidene fluoride) type resin, polyacrylonitrile type resin, poly (vinyl acetate) typeresinandpoly(ethyleneterephthalate) typeresin.
The materials for forming the film (A) on the surface of the signal enhancing material may be the same as those mentioned in the paragraph explaining the formation of the film (A) on the surface of the quartz resonator.
It is preferable that the signal enhancing material has a size not to cause gravitational sedimentation within a measuring time with its particle diameter being approximately 200 to 500 nm and that it can maintain a monodisperse state with its surface density of charge being xe2x88x920.274 to xe2x88x920.451 C/m2.
Forming the film (A) on the surface of the signal enhancing material, for example, latex beads is preferably carried out by treating the surface beforehand for modification so as to make it easily combinable with the forming material of the film (A) and then by fixating the film (A).
As such treating methods for modification, for example in the case of a polystyrene copolymerized with acrylamide, a method may be adopted wherein fixation is performed by a crosslinking agent such as NHS by utilization of the carboxyl group presented by the acrylamide modification.
The above-mentioned film (A) is desirably formed uniformly on the whole of the surface of the signal enhancing material. However, it is not necessarily formed uniformly on the surface if it can adsorb the low molecular weight organic compound of detection target and can pinch/capture the low molecular weight organic compound in cooperation with the film (A) provided on the quartz resonator.
[Scheme of Detection Process of the Present Invention]
An outline of a typical process of the present invention is explained based on FIGS. 1 to 2 by taking an example wherein the substance to be detected is porphyrin and a peptide is used as the material for forming a thin film (A) for adsorption of the porphyrin.
In FIG. 2, in the measuring vessel (cell), there is fixed vertically the quartz resonator shown in FIG. 1, the electrode surface of which is provided with a peptide thin film. Further, in the measuring vessel, there are introduced the latex beads shown in FIG. 1 whose surfaces are provided with the peptide thin films. When porphyrin is put into this measuring vessel (cell), the porphyrin, as shown in FIG. 1, is bound and captured in a sandwich manner between the peptide thin film provided on the quartz resonator and the peptide thin films provided on the latex beads. For this reason, together with the porphyrin, a much larger mass of the latex beads compared with the porphyrin is adsorbed on the quartz resonator. An increase in signal due to this large mass links to a significant decrease in signal of the oscillating frequency of the quartz resonator. By measuring and calculating this signal with the oscillating circuit unit and analyzing device shown in FIG. 2, the porphyrin concentration can be detected with high sensitivity.
The reason is not clear at present, however it is conceived that attributable are formation of a coagulation block of the latex beads through porphyrin bond and physical adsorption of the latex beads gathering nearby the electrode onto the electrode.
According to the detection method of the present invention, detection of a low molecular weight compound in a solution which has heretofore been considered difficult can be achieved in a way with a highly enhanced sensitivity.
This specification includes part or all of the contents as disclosed in the specification of Japanese Patent Application No. 2000-261373 which is the base of the priority claim of the present application.